Grand Inquisitor vs Aayla Secura

Canon and Legends feats for Secura
who wins?

TGI

Aayla's Legends feats give her an edge here. She's defeated Legends Aurra Sing, who performed well against both Qui-Gon and Obi-Wan at the same time. While I wouldn't put Aurra in the same league as TPM Maul (Aurra chose to retreat after briefly holding an upper hand against Obi-Wan and Qui-Gon, stating that they were more than she'd bargained for), this is still a respectable feat. On top of that, Aayla has pretty consistently held her own in duels against Quinlan Vos, who is a very formidable duelist. Meanwhile, the Grand Inquisitor's best dueling feats have been pressuring Vader while Vader was simply testing his reconstructed suit, decisively beating Jocasta Nu, and consistently holding an edge against Kanan long before Kanan's prime. Aayla's showings are more impressive in general, and she should have somewhat of an advantage as a duelist.

When it comes to the Force, the Grand Inquisitor's repeated ragdolling of Kanan with TK is more impressive than Aayla Force pushing Aurra Sing once. However, Aayla has displayed a much wider variety of Force powers. The Grand Inquisitor is likely more powerful between the two, and he's been shown to fall back on the Force frequently, employing it once or twice in pretty much every duel he took part in throughout Rebels. On top of that, nearly every time the Grand Inquisitor uses the Force in Rebels, it takes out the opponent for several seconds, if not minutes at a time. Aayla doesn't utilize the Force in combat nearly as frequently as the Grand Inquisitor, and when she does, it doesn't normally have as great of an effect as the Grand Inquisitor's usage typically does. 

Now that I've put some thought into it, I'm pretty sure Aayla would pressure the Grand Inquisitor in a duel, but he'd probably take her out with his superior TK. His Force pushes almost always knock Kanan out for several seconds or minutes, and Kanan would have died several times over if it weren't for Ezra's intervention. A single powerful Force push from the GI might be enough to end the encounter. And even if it isn't, he might be able to just pin Aayla in place the same way he did to Kanan during their duel at the communication tower.

Legends Aayla holds out one hand